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    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      ol li:first-child {
        color: red;
      }
      ol li:last-child {
        color: blue;
      }
      ol li:nth-child(3n+2) {
        color: green;
      }
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  </head>
  <body>
    <ul>
      <li>家用电器</li>
      <ol>
        <li>冰箱</li>
        <li>洗衣机</li>
        <li>空调</li>
      </ol>
      <li>清洁用品</li>
      <ol>
        <li>洗衣液</li>
        <li>消毒液</li>
        <li>洗厕液</li>
      </ol>
      <li>妇婴用品</li>
      <ol>
        <li>奶粉</li>
        <li>纸尿裤</li>
        <li>奶瓶</li>
      </ol>
    </ul>
  </body>
</html>
